The invention relates to a novel process for the preparation of alk(en)ylphosphoric ester salts.
Alk(en)ylphosphoric esters have excellent properties as detergents, and also a high emulsifying power and good ecotoxicological compatibility.
Of increasing importance is the use of solid, solvent-free phosphoric esters, in particular salts thereof, which, due to their neutral pH values, are very well tolerated by the skin and are advantageous as emulsifiers in cosmetic and pharmaceutical formulations.
The alkyl- and alkenylphosphoric esters are prepared in a known manner by reacting tetraphosphorus decaoxide and fatty alcohols to form mono- and diesters with small fractions of triesters. The phosphoric esters are dissolved in solvents for neutralization, and then reacted with bases, for example NaOH or KOH.
JP 62 198 690 describes the neutralization of phosphoric esters in a hydroxyl-containing, water-soluble reaction medium, for example propylene glycol.
For economical, ecological and performance reasons it would be desirable to find a solvent-free method for the preparation of alk(en)ylphosphoric ester salts.
Surprisingly, it has now been found that alk(en)ylphosphoric esters in the form of their melts can be neutralized with a concentrated aqueous or solid base to give alk(en)ylphosphoric ester salts.
Since the alk(en)ylphosphoric esters are not dissolved in a solvent, subsequent stripping off of same is unnecessary. Moreover, the residual water content in the alk(en)ylphosphoric ester salt can be minimized such that it is bonded as water of crystallization and does not have to be stripped off.
The invention provides a process for the preparation of alk(en)ylphosphoric ester salts of the formula (I) and/or of the formula (II) 
in which
R1 and R2 are identical or different and, independently of one another, are a linear or branched alkyl or alkenyl radical having 6 to 30 carbon atoms and Xn+ is a cation with the valency n, where n is an integer, which comprises reacting alk(en)ylphosphoric esters of the formula (III) and/or of the formula (IV) 
in the form of their melts with a base from which the cation Xn+ arises.
It may be expressly noted that the term base also includes mixtures of chemically different bases. In this case, the alk(en)ylphosphoric ester salts of the formulae (I) and (II) regularly contain different cations Xn+, which arise during the neutralization from the various bases.
The radicals R1 and R2 are preferably alkyl or alkenyl radicals having 8 to 22 carbon atoms.
The alk(en)ylphosphoric esters of the general formulae (III) and (IV) are generally prepared by condensation of phosphorus pentoxide or orthophosphoric acid with fatty alcohols.
Preferred fatty alcohols are caproic alcohol, caprylic alcohol, 2-ethylhexyl alcohol, capric alcohol, lauryl alcohol, isotridecyl alcohol, myristyl alcohol, cetyl alcohol, palmoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, linolyl alcohol, linolenyl alcohol, elaeostearyl alcohol, arachyl alcohol, gadoleyl alcohol, behenyl alcohol, erucyl alcohol, brassidyl alcohol and mixtures thereof.
The preparation of the alk(en)ylphosphoric esters often produces mixtures of mono-, di- and triphosphoric esters, the pH of which is usually in the range 2 to 5.
Of preference for the reaction are mixtures with a monophosphoric ester fraction greater than 60% by weight, preferably greater than 80% by weight. Fractions of triphosphoric esters do not interfere in the reaction.
The alk(en)ylphosphoric esters are preferably melted in a mixing-kneading reactor.
The bases may be organic or inorganic bases which are suitable for neutralizing the OH groups of the alk(en)ylphosphoric esters.
The base may be used as an aqueous solution, preferably as a concentrated aqueous solution, suspension or in the form of a powder. The concentration of the aqueous solutions/suspensions is preferably greater than or equal to 25% by weight, particularly preferably 50% by weight, especially preferably 75% by weight.
In a preferred embodiment, the total amount of water which originates from the base and/or the water of neutralization is such that it is bonded as water of crystallization in the solid phosphoric ester salt.
In a preferred embodiment, the base is used as a saturated aqueous solution. In the case of saturated aqueous solutions, a sufficiently good miscibility of the reactants with the simultaneous minimal introduction of water into the reaction mixture is ensured.
If the base is used in the form of a powder, this has the advantage that no water is introduced via the base, and the water formed during the crystallization is bonded as water of crystallization the solid phosphoric ester salt. Subsequent removal of residual water from the product can be dispensed with.
Preferred bases are metal hydroxides, metal oxides, ammonia, primary amines, secondary amines, tertiary amines, alkanolamines and/or amino acids. Preferred metal hydroxides are alkali metal hydroxides, preferably NaOH and KOH, alkaline earth metal hydroxides, preferably Ca(OH)2, and alkaline earth metal hydroxides, preferably Al(OH)3.
Preferred amines are primary amines with long-chain alkyl or aryl radicals having 6 to 30 carbon atoms, particularly preferably 16 to 22 carbon atoms.
Preferred alkanolamines are monoethanolamine, diethanolamine and triethanolamine.
Particularly preferred bases are alkali metal hydroxides, particularly preferably NaOH and KOH, very particularly preferably KOH.
Accordingly, the cations Xn+ in the formulae (I) and (II) are preferably metal ions, NH4+ and ammonium ions derived from amines, alkanolamines and amino acids. Preferably, n has the value 1, 2 or 3, particularly preferably 1 or 2, very particularly preferably 1.
The equivalent molar ratio of phosphoric ester(s) to base is preferably in the range 1:0.1 to 1:10, particularly preferably 1:0.5 to 1:2, especially preferably 1:0.9 to 1:1.1. Very particularly preferably, the ratio is 1:1.
The reaction of the alk(en)ylphosphoric ester with the base preferably takes place at temperatures of from 50 to 300xc2x0 C., particularly preferably 100 to 180xc2x0 C., over a period of from 0.1 to 10 hours, particularly preferably 0.1 to 5 hours, especially preferably 0.1 to 3 hours.
Advantageously, the reaction temperature is above the melting point of the end product, since sufficiently miscibility of the reactants is then ensured.
The alk(en)ylphosphoric esters are preferably initially introduced as melts and then reacted with the base.
The reaction is preferably carried out with mixing/kneading, preferably in a mixing-kneading reactor.
Surprisingly, it has been found that the quality and processability of the products increases if the reaction mixture is mixed/kneaded following the reaction at 50 to 300xc2x0 C. for a further 0.1 to 6 hours at room temperature.
The mixing/kneading preferably takes place in a mixing-kneading reactor.
The products which are produced can be readily drawn off as a block product or flaked to give a flaked product or be drawn off in the form of pellets.
The alk(en)ylphosphoric ester salts prepared according to the invention are suitable for use in cosmetic and pharmaceutical formulations, in particular for the preparation of oil-in-water emulsions, but also of water-in-oil emulsions. They are preferably suitable for the preparation of alcohol-free emulsions.
The alk(en)ylphosphoric ester salts are usually used in amounts of from 0.1 to 10% by weight, preferably 0.3 to 4% by weight, based on finished formulations.
The emulsions can be used as skincare compositions, such as, for example day creams, night creams, care creams, nutrient cream, body lotions, ointments and the like. Further auxiliaries and additives which may be present are, inter alia, oily bodies, coemulsifiers, superfatting agents, fats, waxes, stabilizers, biogenic active ingredients, glycerol, preservatives, dyes and/or fragrances.
The examples below serve to illustrate the invention in more detail without, however, limiting it thereto. All percentages given are percentages by weight.